As a related art technique in which a piston pin and a crank pin of a reciprocating internal combustion engine are connected by a multi-link piston crank mechanism, Patent Document 1 which applicant of the present invention have proposed is known. The multi-link piston crank mechanism has an upper link which is connected to the piston pin of a piston, a lower link which connects this upper link and the crank pin of a crank shaft, and a control link whose one end is rockably supported at an engine body side and whose other end is connected to the lower link. The upper link and the lower link are rotatably (pivotably) connected through an upper pin. The control link and the lower link are rotatably (pivotably) connected through a control pin.
Regarding the upper pin in such multi-link piston crank mechanism, both end portions of the upper pin are supported at a pair of upper-pin pin boss portions formed at one end of the lower link and having a bifurcated shape, and a cylindrical upper link side pin boss portion of an end portion of the upper link is rotatably (pivotably) fitted or connected to a middle portion in an axial direction of the upper pin.
Patent Document 1 discloses a lubrication structure in which an oil hole is formed at a lower portion of the upper link side pin boss portion so as to penetrate the lower portion along a radial direction, and a part of lubricating oil injected from an oil jet that is disposed at a lower side with respect to the crank shaft is taken in from the oil hole, then the upper pin is lubricated.
In a case of the lubrication structure of Patent Document 1, however, the lubricating oil is supplied only for a limited time period when an injection direction of the oil jet is identical with the oil hole in a state in which the lower link is rocking. It is therefore difficult to continuously supply the lubricating oil to the upper pin.